This project has two overall objectives: (1) evaluation and refinement of rapid cine phase contrast (Spiral-PC) magnetic resonance imaging (MRI) for accurate, noninvasive measurement of renal blood flow (RBF) in humans; and (2) evaluation of the role of PC-MRI in the diagnosis of renal ischemia due to renal artery stenosis (RAS) that causes renovascular hypertension (RVH), and azotemia due to chronic ischemic nephropathy. Spiral-PC uses spiral K-space trajectories which allow it to be very rapid and have high spatial and temporal resolution. It may be optimal, therefore, for in vivo measurement of RBF since acquisition in a single breathhold interval is necessary. Refinement and optimization of Spiral-PC, and of the measurement of volume flow with analysis software, will be performed initially in phantoms in which flow in renal arteries and veins will be simulated. In vivo validation studies of the accuracy of Spiral- PC for measurement of RBF will be performed in normal subjects who will also have RBF determined by a technique of PAN clearance. Hypertensive and/or azotemic patients with RAS documented arteriographically will have Spiral-PC measurement of RBF, both pre- and post-amino acid infusion (known to raise RBF in normals by 20-30%), MRI-determined renal volumes, and solute clearance studies prior to and following angioplasty or revascularization. The applicants proposed to correlate clitucal response of patients in terms of blood pressure decrease, and increase in GFR with pre-intervention parameters determined by magnetic resonance for each kidney (RBF, RBF/unit renal volume, percent increase in RBF following amino acid infusion), and evaluate the predictive ability of these parameters for patient response to intervention. Yearly follow-up exams in treated patients will include Spiral-PC studies and arteriograms, which will be correlated to determine the potential utility of Spiral PC in detecting restenosis of renal arteries.